This present invention relates to an improvement in a molding apparatus, and more particularly to injection molding.
Conventionally to mold plastic products a user must craft a molding apparatus having a ‘top’ portion [core] and a ‘bottom’ portion [cavity]. Typically these portions [core and cavity] are vertically disposed such that they stand side to side with one portion being fixed and stable and the other portion being movable. The cavity side generally houses one or more cavity components and the core side generally houses an equivalent number of core component. Typically the cavity side is the stable side and the core side is the moving side. The cavity side houses the flow channels through which liquified plastic flows through and into the abutting cavity and core sides and houses the heating elements to generate the heat necessary to maintain the liquidity of the plastic material. Each side also has water ducts or channels through which water heated from an outside source passes thereby heating the respective side as necessary.
In operation, the moving side is pushed and pressed into the stable side. A seal is formed where the two sides meet. The cavity side has a pocket into which the core of the core side fits. Cuts are made in the core or in the pocket or both to form the desired finished product. If the cuts are both in the pocket and core, these cut or voids are to correspond to one another and provide the avenues of flow for the liquified plastic. This void form will be referred to herein as the cavity-core mold. The cavity-core mold represents the desired finished product after liquified plastic has been forced thereinto and permitted to cure/cool as necessary. A seal between the cavity side and the core side prevents the liquified plastic from escaping from the cavity-core mold so established.
Each side is heated to a prescribed temperature to accept the flow of liquified plastic. The heating process typically entails the use of water being received from and heated by an external source. The heated water is forced into the mold through the water channels in the mold. The liquified plastic is forced through a flow channel on the stable side and into the cavity pocket and core flowing into and filling the cavity-core mold therein. Heating elements, separate from the heated water and its conduits, in the molding apparatus maintain a prescribed heat to maintain the liquidity and flow of the plastic into the cavity-core mold. Typically, water [and therefore, mold] temperatures range from approximately 120° to approximately 180° [all temperatures herein, unless otherwise stated, are represented in terms of Fahrenheit]. These temperatures will vary depending on the type of material being used to generate the finished product. The water is also used, as necessary to cool the mold as needed. Typically, for thicker products, a lower temperature is sufficient; whereas for thinner products, a higher temperature is necessary to maintain the liquidity of the plastic. The liquified plastic entering the flow channels enters at a temperature ranging from approximately 380° to approximately 440°; depending on the type of plastic being used.
The molding apparatus is made of metal and is heat-conductive and heat-retentive. The natural properties of such heat cause the molding apparatus and its component parts to expand when heat is applied. To limit the adverse effects of expansion, experience has found that the maximum number of cavity-core components on each side of a mold should be four; again, this all depends on the size and type of the desired finished product. In the case of producing strawberry mesh baskets, the maximum is four. Typically, therefore, on the stable side, there are four cavity components abutting one another held firmly in place down and inside the mouth of a cavity plate and on the moving side, and there are four corresponding core components firmly held in place in a core plate. The heat expands the various components, the various components press against adjacent components during expansion, and against the side walls of the mouth of the cavity plate. After time, will crack one or more component parts of the molding apparatus. Use of four cavity-core paired components has reduced, though not eliminated, damages caused by heat expansion. Using more than four such paired components with the cavity components down and inside the mouth of a cavity plate requires a larger cavity plate. Use of more than four will increase production but also, because of the required size of the cavity plate it has been found to cause damage to the molding apparatus sooner. Such, therefore, is not practical under the current art configurations of the molding apparatus.
The component parts for a molding apparatus are costly to produce and consequently to replace. A delicate temperature balance must be maintained to prevent such damage for as long as is possible. Heating channels in the cavity plate also can act to cool the plates as the water flowing through the channels may be regulated to be less than the heat of the plastic and in the respective plates in attempts to maintain this delicate balance. If the plates are cooled too much, the liquified plastic will lose some of its properties prior to being cured resulting in an inferior or unacceptable finished product.
Another problem associated with multiple cavity-to-core components as described above is that, through expansion and contraction, the fit between the cavity component and the core component [pocket-to-core fit or cavity-core mold] may not be as precise as is necessary to create the desired finished product. This is particularly the case when the product desired is a container having a bottom and upstanding perimeter sides, all of which [bottom and sides] are to be mesh-like; i.e., thin strips of plastic with significant spacing between which form the container. Akin to a mesh screen with the mesh openings being significantly large. The shape of the strips may form square-like or diamond-like shapes or any shape desired. Containers such as these are typically used in supermarkets for housing strawberries for example. The use mentioned here is illustrative only and not limitational.
The molding apparatus here requires precision manufacture and precision execution for the desired product to be realized. To this end, grooves are generally cut onto the exterior of the core with no grooves on the interior of the cavity pocket [as described earlier, grooves may also be cut onto the exterior of the cores with corresponding grooves cut within the interior of the cavity; though, for the description which follows, only the core elements is cut]. The grooves or voids on the core will be referred to herein as the cavity-core mold. In those areas where there are no grooves cut on the core then, the core, when pressed into the pocket, will be flush on the pocket surface with no spacing between thereby preventing any liquified plastic to flow thereinto. These sections will form the basis of the ‘holes’ in the mesh-like container. When the moving side of the mold engages the stable side of the mold, the cavity and core components are relatively flush with one another except for the grooves cut into the core. It is into these grooves that the liquified plastic is forced and which forms the desired container. If the fit between the core component and the cavity component is not precise when the moving side is pressed into the stable because, as is typically the case, of expansion which leads to minor misalignment between the centers of the core component and the cavity component, a slightly greater void is formed on one or more sides of this ‘fitted’ cavity-core mold. The portions of the pocket and core which should be flush are not. As liquified plastic is forced into the fitted mold, more plastic than is desired flows into the larger void. The result is a container not having uniform meshing; i.e., some of the desired holes between the plastic strips is partially or completely filled in. This is not the desired result and also results is use of more plastic material than necessary.
No one has been able to significantly reduce the heat-expansion problems addressed above, nor can anyone control the natural expansion associated with heat application, nor has anyone been able to significantly cure the misalignment problem associated with heat expansion of prior art mold apparatus configurations. The natural properties of materials are such that they will expand with heat and contract with cold. The present invention has addressed these matters and has cured these deficiencies by accommodating for heat expansion and misalignment associated therewith by configuring a molding apparatus having a floating cavity component or a floating core component or both.
The foregoing has outlined some of the more pertinent objects of the present invention. These objects should be construed to be merely illustrative of some of the more prominent features and applications of the intended invention. Many other beneficial results can be attained by applying the disclosed invention in a different manner or by modifying the invention within the scope of the disclosure. Accordingly, other objects and a fuller understanding of the invention may be had by referring to the summary of the invention and the detailed description of the preferred embodiment in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.